The present invention relates to a connector device for a transmission path connecting two members relatively rotating at a limited rotational frequency.
Disclosed in U.S. Pat. No. 4,744,763 is a "Connecting Device for a Transmission Line Connecting Two Relatively Rotating Members," in which the transmission line transmits electrical signals or electric power between a rotating member and a stationary member relatively rotating within a limited rotational frequency.
As shown in FIGS. 1 and 2, this conventional connector device comprises a movable housing 10 having a flange portion 1a and mounted on a rotating member, a fixed housing 2 having a flange portion 2a and mounted on a stationary member, a belt-shaped transmission line 3 coiled in a convolution having a plurality of turns around a rotating shaft of the rotating member, and a vibration restraining member 4 interposed between the transmission line 3 and the flange portion 1a or 2a. The transmission line 3 is coiled and loosely housed in a holding portion 5 which is defined by the two housings 1 and 2. The inner and outer coil end portions of the transmission line 3 are fixed to the movable housing 1 and the fixed housing 2, respectively. As the transmission line 3 is tightened or loosened, the movable housing 1 can rotate relatively to the fixed housing 2, for a plurality of turns in an alternating manner. The vibration restraining member 4 restrains the transmission line 3 from vibrating, thereby preventing production of noises.
The connector device of this type may, for example, be used in an airbag apparatus, which is stored in the central portion of a steering wheel of a car steering system, and is adapted to inflate, thereby preventing a driver from bumping against the front portion of the interior appointments, in case of a car crash. The inner coil end portion of the transmission line 3 stored in the holding portion 5 is connected to a lead wire which extends from a starter of the airbag apparatus, while the outer coil end portion of the line 3 is connected to a lead wire which extends to a crash sensor attached to the car front. A start signal from the crash sensor, which serves to start the airbag apparatus, is transmitted by means of the transmission line 3.
In the connector device of this type, unlike a connector device of the slip-ring type, there is no instantaneous disconnection of contacts. In other words, apparatuses on the sides of the rotating and stationary members are always connected electrically with each other without regard to the rotation of the housings 1 and 2, as long as the housings 1 and 2 can rotate relatively. With use of the connector device of the slip-ring type, a short circuit may be caused by metal powder which is produced by a slip ring and a brush in sliding contact with each other, or the apparatuses may undergo wrong operation due to noise signals attributable to the instantaneous disconnection of the sliding contact portions. The connector device of the aforementioned type, however, is free of such awkward situations, thus ensuring formation of a highly reliable transmission path.
In the connector device, the transmission line 3 is loosely housed in the holding portion 5 so that it can tighten or loosen, in order to secure a predetermined rotational frequency of the rotating member relative to the stationary member. Therefore, the transmission line 3 must be longer than a length which is determined by the circumferential length of the holding portion 5 and the rotational frequency of the movable housing 1. Further, the transmission line 3 should be a flexible, seamless integral product which can be smoothly tightened or loosened. In the existing circumstances, therefore, the manufacturing cost is high. Thus, the connector device using the volute transmission line 3 is expensive due to the length of the transmission line.
If the transmission line 3 is lengthened, the whole device is increased in size and weight. Therefore, the operation of the connector device requires a greater torque and produces higher noises. Thus, the connector device cannot enjoy smooth and silent operation.
If the torque increases, moreover, the transmission line 3 is subjected to a greater stress, so that it is liable to be buckled. Once the buckling occurs, it grows into a habit with the transmission line 3. After prolonged use, therefore, buckled portions may become fatigued, thus entailing disconnection.